This invention relates to a fluid-pressure driving device suitable for use with equipment which requires a high-speed operation and a high degree of responsiveness, such as a circuit breaker.
Generally, a circuit breaker requires a high-speed operation. Ever-increasing demand for a supply of electricity and a resultant increase in transmission capacity have made it necessary in recent years for circuit breakers to have an increased capacity to handle a higher voltage. At the same time, they are required to effect breaking at high speed or to reduce the length of time required for effecting breaking, in order to ensure transient stability of the system. To achieve a reduction in the length of time required for effecting breaking makes it essential to shorten the length of time in which an arc is struck in the breaking section and to increase the speed at which the fluid-pressure driving device operates to bring contacts into and out of engagement with each other in the breaking section.
One type of fluid-pressure driving device known in the art used with a circuit breaker comprises, as disclosed in U.S. Pat. No. 4,289,063; for example, an operating cylinder for producing a driving force, a main control valve for controlling the direction of movement of the cylinder and a pilot valve for controlling the main control valve. It has hitherto been customary to fabricate the operating cylinder, main control valve and pilot valve as separate entities and assemble them together by connecting them through pipes or by bolts.
In this type of fluid-pressure driving device, the operating cylinder and main control valve would become larger in size when it is required to develop a high driving force. When it becomes necessary for the fluid-pressure driving device to operate at high speed, the main control valve would become still larger in size and the movable parts would have enhanced inertia, resulting in a slower speed of operation. Besides, it would become necessary to increase the size of the pilot valve, too. Thus, if the operating cylinder, main control valve and pilot valve were fabricated as separate entities and assembled together as has hitherto been the case, the channels connecting them together would become great in length and the transmission of pressure would be delayed or the resistance offered by the channels to the flow of the fluid would increase, making it impossible for the circuit breakers to operate at high speed with a high degree of responsiveness.